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MBChB YR2 MSK > Disease Profiles: Muscle Diseases > Flashcards

Disease Profiles: Muscle Diseases Flashcards

1
Q

What is myasthenia gravis?

A

Severe autoimmune neuromuscular disorder characterised by severe muscular weakness and progressive fatigue

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2
Q

What is MRI used for in suspected polymyositis or dermatomyositis?

A

Used to localise the extent of muscle involvement

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3
Q

Which patient group is most likely to develop myasthenia gravis?

A

Can occur at any age but usually presents at after middle age - most commonly 60-70

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4
Q

Which type of hypersensitivity is myasthenia gravis associated with?

A

Type II

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5
Q

What causes polymyositis and dermatomyositis?

A

CD8+ T cell mediated reaction against muscle antigens

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6
Q

Describe the management of tetanus

A

Surgical debridement, anti-toxin, supportive measures (e.g. benzodiasapines, beta blockers), 7-10 days antibiotics, booster vaccination

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7
Q

Name the two inflammatory myopathies

A

Polymyositis and dermatomyositis

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8
Q

Describe the non-pharmacological management of fibromyalgia

A

Education, graded exercise, CBT, complementary medicine e.g. acupuncture

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9
Q

Describe MRI changes seen in polymyositis or dermatomyositis

A

Muscle inflammation, oedema, fibrosis and calcification

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10
Q

What is polymyositis?

A

Idiopathic inflammatory myopathy that causes symmetrical, proximal muscle weakness

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11
Q

What is usually the first line treatment for myasthenia gravis (if not associated with a thymic tumour)?

A

Anticholinesterases

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12
Q

What is usually the second line treatment for myasthenia gravis (if not associated with a thymic tumour)?

A

Immunosuppressive drugs, corticosteriods

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13
Q

Which bacteria is associated with pyomyositis in contaminated wounds?

A

Clostridium

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14
Q

What are the antibodies associated with polymyositis and dermatomyositis?

A

Non-specific - ANA, anti-RNP

Myositis specific - Anti-Jo-1, anti-SRP

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15
Q

Name the enzymes normally raised in patients with polymyositis or dermatomyositis

A

Muscle enzymes e.g. creatine kinase

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16
Q

What is the definitive test for polymyositis or dermatomyositis?

A

Muscle biopsy

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17
Q

Describe the pathophysiology of myasthenia gravis

A

anti-AChR antibodies are generated in response to AChR subunits expressed by thymic myoid cells (via CD4+ TH cells and B cells)

The anti-AChR antibodies block the binding of ACh to the ACh receptors at the neuromuscular endplate

Endplate potential is not sufficient to trigger muscular contraction

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18
Q

Name a complication of polymyositis and dermatomyositis and name which patient group is most at risk

A

Increased risk of malignancy

Greatest risk in males > 45 years

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19
Q

Which is the most common causative organism for pyomyositis?

A

Staphlococci (90%)

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20
Q

Describe how tetanus can be prevented

A

Routine vaccination, good wound management

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21
Q

Describe the clinical presentation of polymyositis and dermatomyositis

A

Symmetrical, proximal muscle weakness in the upper and lower extremities, insidious onset and gets worse over months

Myalgia in 25-50%

Muscle wasting

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22
Q

Describe a positive muscle biopsy for polymyositis or dermatomyositis

A

Perivascular inflammation and muscle necrosis

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23
Q

What causes myasthenia gravis?

A

Autoimmune disorder - 90% idiopathic, 10% due to thymic tumour

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24
Q

Which patient group does polymyositis and dermatomyositis most commonly occur in?

A

Females age 40-50 years

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25
Q

What is pyomyositis?

A

Acute intramuscular infection secondary to haematogenous spread of the microorganism into the body of a skeletal muscle, most commonly caused by Staph. aureus

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26
Q

Name the gene complex associated with a genetic predisposition for myasthenia gravis

A

HLA associations

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27
Q

Describe the pathophysiology of fibromyalgia

A

Thought to be a disorder of central pain processing or a syndrome of central sensitivity - patients have lower threshold for pain and other stimuli e.g. heat

Can begin after trauma (emotional or physical)

28
Q

What is dermatomyositis?

A

Idiopathic inflammatory myopathy that causes symmetrical, proximal muscle weakness, and cutaneous manifestations

29
Q

Which organism is associated with myonecrosis?

A

Clostridium perfringens

30
Q

What does imaging (x-ray, CT or MRI) typically show in myonecrosis?

A

Feathering pattern of soft tissue

31
Q

Describe the management of myonecrosis

A

Immediate surgical debridement and antibiotic therapy

32
Q

Describe the clinical presentation of fibromyalgia

A

Persistent (≥ 3 months) widespread pain on both sides of the body, above and below the waist, includes the axial spine and chest pain (non-cardiac)

Fatigue - disrupted and unrefreshing sleep

Headaches, cognitive and memory impairment, anxiety and depression

33
Q

Describe the clinical presentation of pyomyositis

A

Pain and swelling of the affected area (usually lower extremities), fever

34
Q

Name two conditions which have been associated with fibromyalgia

A

RA, SLE

35
Q

Which investigation would you perform in suspected tetanus?

A

Wound culture

36
Q

What would you expect to see in a wound culture from a patient with tetanus?

A

Anaerobic gram positive with terminal spore

37
Q

Name three cutaneous features of dermatomyositis

A

Gottron’s sign, heliotrope rash, shawl sign

38
Q

What is the mechanism of action of anticholinesterases for myasthenia gravis?

A

Increase neurotransmission by increasing the concentration of ACh in the synaptic cleft

39
Q

How would you diagnose fibromyalgia?

A

Diagnosis of exclusion - patient experiences widespread pain and associated symptoms, symptoms at the same level for ≳3 months and there is no other explanation

40
Q

Which antibody is associated with the development of interstitial lung disease in patients with polymyositis or dermatomyositis?

A

Anti-Jo-1

41
Q

What is tetanus?

A

Acute disease caused by neurotoxins from the bacterium Clostridium tetani

42
Q

When is a thymectomy indicated in myasthenia gravis?

A

When MG is associated with a thymic tumour - first line if indicated

43
Q

Describe possible electromyography findings in patients with polymyositis or dermatomyositis

A

Increased fibrillations, abnormal motor potentials, complex repetitive charges

44
Q

What is fibromyalgia?

A

Neurosensory disorder characterised by chronic MSK pain

45
Q

Describe the clinical presentation of myonecrosis

A

Disproportionate muscle pain, massive edema with skin discoloration

May be no fever or cutaneous manifestations but can rapidly progress to systemic infection (within hours)

46
Q

What is viral myositis?

A

Muscle inflammation due to a viral infection e.g. influenza, enteroviruses, HIV, HTLV, CMV, rabies, dengue

47
Q

Which patient group is most likely to develop fibromyalgia?

A

Commonest cause of MSK pain in women 22-50

48
Q

Describe the clinical presentation of tetanus

A

Trismus (lock jaw), risus sardonicus, autonomic instability

49
Q

Which bacteria are associated with pyomyositis in immunosuppressed patients?

A

Psudomonas, beta haemolytic strep. enterococcus

50
Q

Which class of bacteria is associated with pyomyositis in the perineum?

A

Gram-negative bacteria

51
Q

Describe the clinical presentation of viral myositis

A

Muscle pain, tenderness, swelling and often weakness, typically after a few days of fever

52
Q

Which investigations would you perform in suspected myonecrosis?

A

X-ray, CT or MRI

Lab tests - Gram staining, wound culture, blood culture

53
Q

What two examination tests would you perform in suspected polymyositis and dermatomyositis?

A

Confrontational testing (of power)

30 second sit to stand test

54
Q

Define myopathy

A

Disease of the muscle in which the muscle fibres do not function properly

55
Q

Describe the management of viral myositis

A

Symptomatic

56
Q

How would you manage patients with polymyositis or dermatomyositis?

A

Prednisolone treatment of choice - aim to gradually lower dose, eventually stop

Alternative treatments if not responsive: immunosuppression e.g. azathioprine, methotrexate, IV immunoglobin, rituzimab

57
Q

Describe the management of pyomyositis

A

Antibiotics and surgery (debridement)

58
Q

Which investigations would you perform for suspected myasthenia gravis?

A

Lab tests - anti-AChR IgG in serum

Repetitive nerve stimulation - gradually reducing responses indicates NMJ dysfunction

59
Q

Why can myasthenia gravis be life-threatening?

A

In advanced stage all muscles are weak → life-threatening impairment of respiration

60
Q

Describe the pathophysiology of tetanus

A

C. tetani spores found in soil, enter the body through broken skin

After incubation (4 days to several weeks) the toxin binds to inhibitory neurons, preventing release of inhibitory neurotransmitters → widespread activation of motor neurons and spasming of muscles throughout the body

61
Q

Describe the clinical presentation of myasthenia gravis

A

Insidious onset of fatigue and progressive muscle weakness

Muscles of the eyes, mouth, throat and neck usually affected first

62
Q

Which bacteria is associated with pyomyositis in tropical climates?

A

MSSA infection in immune competant patients and children

63
Q

Which investigation would you perform in suspected viral myositis?

A

Bloods - elevated CK

64
Q

What is myonecrosis?

A

Life-threatening necrotizing soft tissue infection commonly caused by the rapid proliferation and spread of Clostridium perfringens from a contaminated wound

65
Q

Describe the pharmacological management of fibromyalgia

A

Anti-depressants e.g. tricyclics, SSRIs

Atypical analgesia including tricyclics (e.g. amitriptyline), gabapentin and pregabalin

MBChB YR2 MSK (36 decks)

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